tty: n_hdlc: use guard()s

Use guards in the n_hdlc code. This improves readability, makes error
handling easier, and marks locked portions of code explicit. All that
while being sure the lock is unlocked.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://patch.msgid.link/20251119100140.830761-5-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Jiri Slaby (SUSE)

drivers/tty/n_hdlc.c

@@ -263,21 +263,18 @@ static int n_hdlc_tty_open(struct tty_struct *tty)
  */
 static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 {
-	unsigned long flags;
 	struct n_hdlc_buf *tbuf;
 	ssize_t actual;
 
 check_again:
-
-	spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
-	if (n_hdlc->tbusy) {
-		n_hdlc->woke_up = true;
-		spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
-		return;
+	scoped_guard(spinlock_irqsave, &n_hdlc->tx_buf_list.spinlock) {
+		if (n_hdlc->tbusy) {
+			n_hdlc->woke_up = true;
+			return;
+		}
+		n_hdlc->tbusy = true;
+		n_hdlc->woke_up = false;
 	}
-	n_hdlc->tbusy = true;
-	n_hdlc->woke_up = false;
-	spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
 
 	tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
 	while (tbuf) {
@@ -324,9 +321,8 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
 		clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 
 	/* Clear the re-entry flag */
-	spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
-	n_hdlc->tbusy = false;
-	spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
+	scoped_guard(spinlock_irqsave, &n_hdlc->tx_buf_list.spinlock)
+		n_hdlc->tbusy = false;
 
 	if (n_hdlc->woke_up)
 		goto check_again;
@@ -585,7 +581,6 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
 {
 	struct n_hdlc *n_hdlc = tty->disc_data;
 	int count;
-	unsigned long flags;
 	struct n_hdlc_buf *buf = NULL;
 
 	pr_debug("%s() called %d\n", __func__, cmd);
@@ -594,26 +589,26 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
 	case FIONREAD:
 		/* report count of read data available */
 		/* in next available frame (if any) */
-		spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock, flags);
-		buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
-						struct n_hdlc_buf, list_item);
-		if (buf)
-			count = buf->count;
-		else
-			count = 0;
-		spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock, flags);
+		scoped_guard(spinlock_irqsave, &n_hdlc->rx_buf_list.spinlock) {
+			buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
+						       struct n_hdlc_buf, list_item);
+			if (buf)
+				count = buf->count;
+			else
+				count = 0;
+		}
 		return put_user(count, (int __user *)arg);
 
 	case TIOCOUTQ:
 		/* get the pending tx byte count in the driver */
 		count = tty_chars_in_buffer(tty);
 		/* add size of next output frame in queue */
-		spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
-		buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
-						struct n_hdlc_buf, list_item);
-		if (buf)
-			count += buf->count;
-		spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
+		scoped_guard(spinlock_irqsave, &n_hdlc->tx_buf_list.spinlock) {
+			buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
+						       struct n_hdlc_buf, list_item);
+			if (buf)
+				count += buf->count;
+		}
 		return put_user(count, (int __user *)arg);
 
 	case TCFLSH:
@@ -720,14 +715,10 @@ static struct n_hdlc *n_hdlc_alloc(void)
 static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
 						struct n_hdlc_buf *buf)
 {
-	unsigned long flags;
-
-	spin_lock_irqsave(&buf_list->spinlock, flags);
+	guard(spinlock_irqsave)(&buf_list->spinlock);
 
 	list_add(&buf->list_item, &buf_list->list);
 	buf_list->count++;
-
-	spin_unlock_irqrestore(&buf_list->spinlock, flags);
 }
 
 /**
@@ -738,14 +729,10 @@ static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
 static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
 			   struct n_hdlc_buf *buf)
 {
-	unsigned long flags;
-
-	spin_lock_irqsave(&buf_list->spinlock, flags);
+	guard(spinlock_irqsave)(&buf_list->spinlock);
 
 	list_add_tail(&buf->list_item, &buf_list->list);
 	buf_list->count++;
-
-	spin_unlock_irqrestore(&buf_list->spinlock, flags);
 }	/* end of n_hdlc_buf_put() */
 
 /**
@@ -758,10 +745,9 @@ static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
  */
 static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
 {
-	unsigned long flags;
 	struct n_hdlc_buf *buf;
 
-	spin_lock_irqsave(&buf_list->spinlock, flags);
+	guard(spinlock_irqsave)(&buf_list->spinlock);
 
 	buf = list_first_entry_or_null(&buf_list->list,
 						struct n_hdlc_buf, list_item);
@@ -770,7 +756,6 @@ static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
 		buf_list->count--;
 	}
 
-	spin_unlock_irqrestore(&buf_list->spinlock, flags);
 	return buf;
 }	/* end of n_hdlc_buf_get() */